The described invention relates in general to welding systems, and more specifically to an accessory for use with arc welding systems, wherein the accessory increases the rate at which welding may occur.
Arc welding is a common category of welding that includes, for example, flux-cored arc welding, submerged arc welding, and gas metal arc welding, all of which are used to weld together materials referred to as base metals. These types of arc welding typically involve the use of a power source for generating heat by creating an electric arc between a consumable electrode (which may be a wire or a strip) and the base metals. The electrode and portions of the base metals melt and then fuse together at a welding point between the base metals. The area around the welding point is typically shielded by gas (which is generally inert for welding purposes) or flux for preventing contamination of the molten metal.
Within the context of commercial welding, a primary objective is the completion of any particular welding job in the shortest time possible without sacrificing weld integrity. An increase in the rate of welding may be accomplished by increasing the current delivered to the electrode from the power source. When more electrical energy is induced by increasing the current delivered to the electrode and the arc, the burn-off rate of the electrode and the deposition rate of the weld are increased. However, larger more expensive power sources are often required to sufficiently increase current levels, making this approach generally less attractive from a cost perspective.
Another approach to increasing the welding rate involves increasing the electrode extension. Electric current is carried by the consumable electrode at the point of electrical contact with a contact tip. The current passes through the consumable electrode to the tip of the electrode to the arc. The distance from the point of the final electrical contact with the contact tip to the electrode's tip at the arc is identified as the “electrode extension”. The electrode is subject to resistance heating based on the formula I2R, where I equals current and R equals resistance. The longer the length of the electrode from the point of electrical contact to the arc or the smaller the cross section of the electrode, the greater the heat buildup within the electrode. This is due to increased electrical resistance. Electrical contact over the electrode extension must be avoided. An electrode heated to a higher temperature melts faster at the arc than a colder electrode melts given the same power input. One problem with electrode extension welding is that if the electrode extension is too long, the heat buildup within the electrode may become too intense and the electrode may lose its stiffness. Such a loss in columnar strength makes positioning of the electrode at the welding location difficult due to wandering of the tip.
As will be appreciated by one of ordinary skill in the art of welding, the net result of increasing the electrode extension is to make the welding process more efficient. When the electrode extension is increased while keeping the welding current constant, the result is a greater quantity of melted electrode and a smaller quantity of melted base metal. As an example, an unguided electrode extension of ¾ inch to 1 inch is commonly used for 3/32 inch diameter wire for submerged arc welding of carbon steel. Successful welding can be performed with electrode extension guides up to at least 3 inches (with 3/32 inch diameter wire) while providing the same current input. Increases in electrode extension are known to result in significant increases (e.g., greater than 75%) in deposition rate for welds. However, electrode extensions are typically maintained at levels of 20% to 60% deposition rate increase to provide weld integrity in most applications. The burn off rate for a 3/32 inch diameter solid carbon steel electrode at a 1 inch electrode extension and 400 amperes (DC+) is approximately 9.5 pounds per hour. The burn off rate for a 3/32 inch diameter solid carbon steel electrode at 2¼ inch electrode extension and 400 amperes (DC+) is approximately 13.5 pounds per hour. Essentially, the benefits of increased electrode extension are known to include: (i) increased electrode melting rate; (ii) lower base metal heat input resulting in narrower heat affected zones; (iii) lower heat input for better control of temperature between weld passes; and (iv) lower heat input for less distortion.
Certain types of electrode extension guides that are intended to prevent electrical contact between the final electrical contact point and the tip of the electrode are known. These guides incorporate a cylinder in one form or another that serves as a guide and that utilizes ceramic (or other insulating material) to avoid electrical contact with the electrode over the length of extension. Ceramics can provide most of the basic properties required for a successful guide, such as high temperature resistance, high wear resistance at high temperature, high thermal shock resistance, and resistance to the flow of electricity. However, a combination of these properties is possessed only by a relative few ceramics, such as lava and silicon nitride materials, which suffer from certain limitations. For example, lava cannot accommodate the highest levels of amperage required for some welds.
Most ceramics provided in cylindrical form lack the mechanical properties necessary to avoid failure due to breakage in the industrial environment, especially due to the dragging of large, cold electrodes on base metals. Another reason for the breakage of cylindrical ceramic components used as electrode extension guides is a delay in the instantaneous full ignition of the arc at weld initiation. This delay may be caused by poor electrical contact or improper adjustment of startup parameters including the starting wire feed speed rate (also known as ‘run in speed’). The mechanical properties of ceramics to be considered for increased durability include tensile strength, impact strength, flexural strength and compressive strength at room temperature and at the elevated temperatures encountered in welding processes. Silicon nitride ceramics possess highly desirable properties (including mechanical properties) when compared to lava and most other available ceramics; however, production of cylindrical forms of silicon nitride useful for electrode extension guides is cost prohibitive. Moreover, cylindrical forms of silicon nitride are still prone to mechanical breakage, especially due to wire dragging.
In addition to certain limitations resulting from the use of the materials previously discussed, existing electrode extension guides suffer from other shortcomings. For example, some guides do not provide adequate guidance to keep the electrode on a narrow line of welding that is often required for a successful weld. Some guides also have a propensity for allowing the heated and softened electrode to collapse within the guide upon weld startup due to excessive inner diameters. Guides with thru holes near in size to the electrode can provide more accurate guidance of the electrode, but are prone to jamming due to the presence of foreign material such as stray welding flux and metal filings produced in the wire feed mechanism. Therefore, there is an ongoing need for an effective, relatively inexpensive, and highly durable electrode extension guide for use in arc welding processes with continuously fed electrodes.